But it's potentially much more than that. It is a web-based, notebook-style, mathematics environment which brings together, under a unified interface, a host of very powerful GPL'd Scientific apps, plus the python language.

Python glues the whole framework together, but is also available as a programming language. There is even version control for notebooks provided by Mercurial.

SAGE is distributed as a fat binary for multiple platforms, so that it can be used immediately upon download. It can also be used on the console but I recommend running the Web interface.

Despite its version number, 2.3, I think the notebook interface could be improved to facilitate access to components. But its a very usable environment for both research and teaching, and has a very extensive documentation set.